THERE WAS A TIME up until the late 1980s when manufacturers could list other brands of “interchangeable” plug-in breakers that could be used in their panels. The PANEL label has to simply list those compatible breakers. So that Arrow-Hart / Murray panel is a prime example of that labeling. Arrow-Hart bought Murray around 1970, then were themselves bought by Crouse Hinds in 1979, so a panel showing Arrow-Hart / Murray was from within that era when interchangeable breakers were allowed.
But that CHANGED after some spectacular field failures (fires) and subsequent lawsuits in the early to mid 80s. The issue was, there were SLIGHT differences in how the different bus and stabs were designed, along with a flurry of industry consolidation to where older panels were no longer being supported by new owners. So UL changed the listing rules in (I think) 1988 or 89 to require that breakers and panels be TESTED AND LISTED TOGETHER. This effectively put an end to interchangeability as it was known then.
But right about that same time, GTE had decided to get into the electrical equipment business and bought Zinsco, which turned into a debacle. So they also bought Sylvania-Clark, and in doing so gained the ability to make a new line of “interchangeable” breakers to get out from under the Zinsco fiasco. They had the Zinsco facility make a new panel system copying the bus from ITE, Bryant and Murray, but had the Sylvania plant make new interchangeable breakers so as to disassociate the breakers from Zinsco. To try to gain market acceptance, those mid-80s Sylvania panels listed virtually every other interchangeable breaker under the sun on their labels, and they marketed the breakers likewise. They were the last to do so.
But when UL changed just a few years later, it threatened to put GTE out of the business they had just heavily invested in. So apparently GTE threatened to sue UL for restriction of trade. The settlement was that UL created the “Classified Breaker” program wherein a BREAKER MANUFACTURER could test their breakers in competitors panels, so that the breakers could be RETROFITTED into existing panels of another brand. But to attain this, GTE /Sylvania had to buy and test virtually every competitive panel on the market at that time, getting “Classification” of their breakers in all of them. That was a huge expense that they hoped would pay off. But it was not good enough to overcome their Zinsco problem, and later bad decision to also buy the rights to FPE from Reliance, so GTE pulled the plug. Not willing to let it all go, managers of the Sylvania plants bought that division and created Challenger. They struggled too (I think from under the weight of still being associated with Zinsco and FPE), to where they went belly up in the 90s. Eaton saw the value of the Classified Breaker product line, so they bought ONLY that product and production facility, which today remains as their “CL” product line. You will note that the CL line is not sold with any panels, it is JUST a line of breakers that can legally be RETROFITTED into existing panels, most notably all most all of the former “interchangeable” panels from now defunct brand names.
So here is how it works now. Under NEC 110.3(b), everything you install for inspection must the listed for the intended use and installed per manufacturer’s instructions. So if you are installing a NEW PANEL, that panel is only listed with its own breakers. Nobody that makes panels is going to pay megabucks to test and list competitive brands of breakers, why would they? But AFTER the fact, if you are needing to RETROFIT a breaker into an EXISTING panel (that was ostensibly installed inspected and approved by virtue of all of the breakers being the same brand), that retrofit breaker CAN be a “Classified” breaker, of which the major supplier is Eaton CL (by way of Challenger / GTE Sylvania). There are other minor players in the Classified breaker business, such as Connecticut Electric / UBI as well. In general, Classified breakers are more expensive than the original breakers for a panel, because the sales volume for them is extremely low in comparison.
What you CANNOT do however is plug a BR breaker into a Siemens panel, or vice-versa, or plug a Square D HOM breaker into ANYTHING other than a HOM panel, or any breaker that is NOT cross-listed**. All of those other combos violate 110.3(b). The EXCEPTION is if it is a pre-change panel, like in the Arrow Hart example, and the panel label is still there and specifically states that the panel can except other breakers.
**Cross-listed is different. Siemens bought ITE in the 80s. ITE was brand-labeling their breakers to Murray/Crouse Hinds already at the time. Siemens later BOUGHT Murray and has not substantially changed the old ITE breakers. So the current Siemens QP breakers are cross-listed to be used in Murray and Crouse Hinds/Murray panels. Murray no longer exists as a separate brand name under Siemens as of I think 2022. At one time if you ran into an inspector who didn’t know this, you could get a letter from Siemens explaining it. I don’t know if that’s still the case.
Disclaimer: This is not meant to be anything more than a general timeline, I no longer remember all of the exact dates. I worked for Siemens for a time and learned most of this from internal documentation that was not available to the public. But as much as I want to think that was just “a little while ago”, it’s approaching 20 years ago now, so I have killed off some of those brain cells.
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